This invention relates to imaging systems, and more particularly, to a improved method and apparatus for developing electrostatic latent images with a liquid developer.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. One conventional process involves placing a uniform electrostatic charge on a photoconductive insulating layer comprising zinc oxide powder and a resinous binder carried on a conductive paper substrate, exposing the layer to a light-and-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a charged toner which is dispersed in an insulating liquid. The charged toner may be suitably colored and may have a polarity of charge identical or opposite to that of the latent image to be developed. If the polarity of charge of the toner is identical to that of the latent image, reversal development will occur whereas a toner having a charge opposite to that of the latent image will be attracted to the latent image. Generally, a development electrode is employed with liquid development processes to eliminate the well-known edge effect. Since the electrostatic field resulting from the electrostatic latent image is relatively strong along the edges of the electrostatic latent image but relatively weak near the center of the electrostatic latent image, a print developed without the aid of a development electrode is characterized by dense toner deposits in the peripheral areas of the electrostatic latent image and relatively little or no toner deposits in the central areas of the electrostatic latent image. In order to eliminate this edge effect, it is necessary to position a development electrode close to the electrostatic latent image bearing surface during development. Generally, the closer the development electrode is positioned to the electrostatic latent image, the greater the reduction of edge effect. Unfortunately, at relatively high development speeds and close development electrode spacings, the deposited toner image tends to form streaks parallel to the direction of relative movement between the photoreceptor surface and liquid developer. Generally, liquid developers contain carrier liquids which are highly volatile and often inflammable. Exposure to the ambient atmosphere of liquid developers containing highly volatile and inflammable components is undesirable because of the danger to the machine operator. Thus, there is a continuing need for an improved imaging system.